Cultivars with greater resistance to grain rot and the use of fungicides are management options to reduce productivity losses, point out research networks that study the topic. Initially called soybean anomaly, the problem has been occurring more frequently in the mid-northern region of the state of Mato Grosso and in Rondônia since the 2018/2019 harvest.
Different species of fungi have been identified in pods and stems with and without symptoms of grain rot, but the factors that trigger the problem are still unknown. Therefore, several multidisciplinary research networks are analyzing data such as climate, fertility and soil physics, lignin content and others that may provide clues about the disease.
The network that evaluates the efficiency of fungicides brings the first results that could assist in disease management strategies, with the launch of the publication “Efficiency of fungicides for the control of soybean grain rot”.
The technical circular “Efficiency of fungicides for the control of soybean grain rot, in the 2022/2023 harvest: summarized results of cooperative trials” (Technical Circular 197), is the result of the fungicide evaluation network formed by Embrapa, Fundação MT, Rio Verde Foundation, Proteplan, Fitolab Agricultural Research and Development, Celeiro do Norte Research Center (CPCEN), EPR Consultoria & Agricultural Research, MZ Consultoria Agronomia, Federal University of Mato Grosso (UFMT-Sinop), Federal University of Rondônia and Solo Fértil .
In parallel, another group evaluated the reaction to rot of 54 soybean cultivars (42 transgenic and 12 conventional) and identified cultivars with good and medium levels of resistance and those that are susceptible to the problem.
Since the 2018/2019 harvest, the problem has been causing losses to producers, especially in the mid-north region of Mato Grosso and Rondônia, which led to the formation of research networks to identify the causes of the problem and define management strategies. “During visits to the region, we observed that the problem affected the cultivars differently and the symptoms responded to treatment with fungicides, which is why networks of cooperative trials were formed to evaluate the sensitivity of cultivars to the disease and the efficiency of fungicides”, reports researcher Maurício Meyer, from Embrapa Soja (PR).
The symptoms initially described as an anomaly correspond mainly to the rot of the grains and pods. Several samples were collected in which a complex of fungi from different species of Fusarium, Diaporthe and Colletotrichum were found in the pods, grains and stems. In some harvests, they also observed a high incidence of purple spot in grains, caused by Cercospora spp. “These fungi can be found latently in the plant and grains (endophytic fungi), without causing apparent symptoms: each associated with a disease when symptoms occur. They were identified even in pods and grains without symptoms”, says Embrapa researcher Cláudia Godoy.
The researcher also explains that, at the onset of symptoms, the pods may appear waterlogged, darkened or both, without a visible opening. When opened, the grains rot. “The presence of pods with symptoms and rotten grains occur randomly on the plant and in the pod, respectively, not necessarily affecting all grains”, she says.
Godoy assesses that the symptoms occur mainly from the grain filling (stage R5), until its maturation (stage R8). According to her, climate-related stress conditions encourage latent fungi to initiate infection. “The factors that trigger the greater frequency of grain rotting by these pathogens in these regions are still under study”, explains Godoy.
In trials carried out at Embrapa Agrossilvopastoril, in Sinop (MT), different species of fungi obtained from pods with symptoms of rot were inoculated on soybean plants in a greenhouse, but to date, none of these isolates have reproduced the symptoms that occur in the plants. in the field.
Researcher Dulânndula Wruck explains that inoculation techniques are also being studied, since some isolates kill the plant days after inoculation when the toothpick technique is used. “So far with the information we have, it is possible that other factors are involved in the manifestation of symptoms, which is why ongoing projects are multidisciplinary, analyzing data such as climate, fertility and soil physics, lignin content, etc.
Practically all research companies located along the BR 163 axis in the mid-north of Mato Grosso are studying the problem. “The results of the fungicide network and cultivars from the 2022/23 harvest are a source of information for the producer, to help manage the problem”, says the researcher.
To evaluate the efficiency of fungicides in controlling grain rot in soybeans, five protocols were carried out in the mid-north region of Mato Grosso and in Rondônia. The treatments used site-specific fungicides (they target a metabolic process of the fungus or a single enzyme or protein necessary for its survival) alone and in mixtures without and with multisite fungicides (they interfere with many metabolic processes of the fungi). “In these experiments, the fungicides were evaluated individually and in sequential applications”, explains Godoy.
During the 2022/23 harvest, the spraying of different fungicides, in network trials, resulted in a reduction in disease symptoms and an increase in productivity. “The use of fungicides favors both the reduction of the incidence of rot symptoms and the control of other diseases, such as target spot - which predominates in the region - which results in improved productivity”, explains Godoy. “We understand that fungicides are an important control tool, and should be defined according to the sensitivity of cultivars to grain rot and other diseases”, he reveals. (see more details in the table below)
In addition to the use of fungicides to manage the disease, researchers advise the adoption of different anti-resistance strategies. They argue, for example, that the information obtained in these studies helps to determine control programs, always prioritizing the rotation of fungicides with different modes of action. They warn that sequential applications with the same active ingredients should be avoided to reduce selection pressure for fungal resistance to fungicides.
For about a year, the cultivar evaluation network, made up of 12 research institutes, universities, cooperatives and foundations, has sought to understand the impact of cultivar choice on the management of grain rot. The results obtained in crops in Sorriso, Nova Mutum, Lucas do Rio Verde, Sinop and in some areas in Rondônia total 3 million hectares.
The network evaluated 54 soybean cultivars (42 transgenic and 12 conventional) and also carried out experiments in three planting seasons. According to researcher Austeclinio de Farias Neto, from Embrapa Cerrados (DF), the cultivars were characterized in terms of their reaction to rot: those that had good levels of resistance, medium levels and those that were susceptible. “With this information, producers will have even more support for their planning, in order to face the problem”, highlights Farias Neto. Detailed results will be released soon.
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